This is not an official news source for CineForm or GoPro product releases, just some bits and pieces of stuff I happen to be working on. My work and hobbies are pretty much the same thing. -- David Newman

Thursday, July 26, 2007

Got that out of the way. It seems that there have been a bunch of forum threads attacking Canon, saying that this awesome little camera doesn't really shoot 24p. Not that misinformation is unusual for the internet, however, these posts often quote me or CineForm as backing this position. Neither myself nor CineForm support these posts or claims.

The problem arose when I did state that there can be a subtle issue for chroma keying when using any 4:2:0 24p signal encoded into 60i. Some users took that and ran with it. I had seen some of this in customer footage, nothing I have shot. I probably wouldn't have mentioned anything other that it is a another selling point to using the HDMI output from these new cameras (which is damn cool), and I'm a video geek. Since then I'm not even sure this issue exists outside of MPEG compression artifacts, as some more recent burrowed footage looks great. I have so little HV20 footage to work from that we shoot ourselves -- Canon, we need a camera longer than a few days -- I want one to take home :).

Basically, the 24p signal is good, and the CineForm pulldown from 1080i60 HDV tape works perfectly. That is my position.

Here is some 24P extracted footage from a friend's HV20 as she was documenting some behind the scenes footage for our 48 Hour Film Project shoot -- the camera pictured is a Silicon Imaging 2K. We intercut the HV20 footage into the credits of this movie and presented it at 1080p24 on a Sony 4K projector. The linked clip is a 110MB 1440x1080 CineForm AVI, so if you need a CineForm decoder for your PC (Mac version coming), you can download one for free from CineForm.com.

P.S. Other HV20 misinformation : when recording the Canon HV20 to tape, the image is 1440x1080, that is the HDV standard used. It is not 1920x1080, you only get that out of the HDMI port, and even then the image is likely upsized from an internal 1440x1080 image (which is still very nice.) The 1920x1080 native image is only available in the still camera mode.

19 comments:

Anonymous
said...

I dont think it was 'some users ran with it,' I think was just myself. I quote a credible source since everyone reacts so defensively when I bring up the infamous '4th frame issue.' Its downright bizarre.

Have been trying for weeks in vain to figure out why I am the only person who sees the HV20 24p footage as poor. HV20 fans get mysteriously riled, & support gets evasive over the weak chroma problem that you have clearly described as resulting in some residual interlacing in the HV20's tape recorded 24p.

You asked me to post an example on DVinfo which I am mysteriously not allowed to post there. Everyone reacts so conspicuously about this topic(?). What is everyone so defensive and afraid of? Just take a look. Tell me where I am wrong?

Here is a clip from my HV20(6.5mb) before 24p conversion. http://www.box.net/shared/static/b7qayhgfqa.mpegHere it is after-http://www.box.net/shared/static/va357ns51c.movMy frame 4 still has interlacing-http://www.box.net/shared/static/6anr20frau.jpgWhat does your frame 4 look like after 24p conversion?

Have yet to figure out how any amount of interlacing can be construed as progressive.

Yes, the data format out of the HDMI port is 1920x1080 4:2:2 YUV 8-bit. What happens early in the processing chain is not known outside of Canon -- I expect the internal processing is 1440x1080 just like it is with the Sony V1.

23.976p seems to be continually the problem, doesn't it? Perhaps the person with the issues tried a 2:3:3:2 inversion as opposed to a 2:3 inversion?

A lot of the HV20 news I've seen is the typical problem when new features get introduced at a consumer price point - confused consumers with no idea about pull-downs, drop frames and interlace. Not that there aren't confused pros...

sound like to me everyone that bought xha1 is probably pissed off that the hv20 that is under 1000 dollars really rivals it,and I have seen amazing footage made from it, people that paid $4000 for that camcorder is in denial about the truth period!!!and honestly I would be too if i own one....

While the results are progressive the encoding is interlaced, so it doesn't matter whether the chroma is 4:4:4, 4:2:2 or 4:2:0, the chroma for each field correctly matches the luma for that field. As each of the fields for luma and chroma are separable, pulldown can be fully reversed.

" CineForm Aspect HD does support automatic extraction of 24p from HV20's 60i stream. However, Ridlen is correct that the 60i encoding of 24p is not completely reversible, whereas the in 24F in the XH-A1 and XL-H1 is it. The reason the lack of completely reversibility is the 4:2:0 60i encoding which has only chroma value for pixels over two scan lines -- these scan lines may contain data from different frames, cause chroma cross-talk. The luminance is perfectly correct. Luma is encoded at 60i, and chroma at 30p, you can extract 24p from luma but not fully from chroma. If the pulldown is extracted correctly, the chroma cross-talk will only appear on every fourth frame. As our eyes are far more sensitive to luma, it is very hard to see this in motion. The only time this can be an issue is when keying, for that I recommend using HMDI and shooting live via the Black Magic Intensity card (using the new 1.5 drivers.) All CineForm tools support real-time pulldown removal using that card from the HV20. When you do a live capture the 24p in 60i is encoded as 4:2:2, with has separate chroma values for each scanlines, now the pulldown is completely reversible.

And I recorrected that in later posts and in many forum discussions on the subject. The mistake made was the confusion of 4:2:0 progressive sampling versus interlaced sampling. The fields are completely separable and therefore the pulldown is reversible